This invention relates to an optical communication system, and is particularly concerned with such a system in which high intensity light is transmitted along a light guide, such as an optical fibre. If a break occurs in the light guide, or if in-line components between a transmitter and a receiver fail, it is necessary to effect a repair. In the past, the intensity of light travelling along a light guide has tended to be fairly low, with a consequently low risk of harm to an operator during the repair. However, as the intensity of light increases, for example in WDM (wave division multiplex) optical communication systems in which light from possibly a large number of high power lasers is transmitted down a common light guide, the risk of injury becomes significant. In the event that a break in the light path is detected, transmission of the light is shut down, but resetting the system so that the transmission of light can be restored safely and without excessive down time is difficult.
The present invention seeks to provide an improved optical communication system.
According to this invention, an optical communication system includes a transmitter and a receiver linked by a light guide, means for transmitting a traffic-carrying optical channel and a supervisory optical channel along said light guide, means consequent upon a malfunction in the light guide for ceasing transmission of the traffic-carrying optical channel and means utilizing the supervisory optical channel to determine when the light guide is reusable for communication purposes.
As the supervisory optical channel is a single optical channel, it can be within the safe limits for personnel handling the broken or damaged light guide, but preferably it operates at a power which is lower than each of the traffic-carrying channels Preferably, following detection of the malfunction, the supervisory optical channel is operated in a pulsed manner. This reduces its mean power to a lower, safe level.
The light guide is preferably an optical fibre. Such fibres can be damaged or broken fairly easily giving rise to a malfunction which prevents proper transmission of data traffic.
The supervisory channel is preferably coupled into the optical fibre downstream of power amplifiers which amplify the traffic-carrying channels to their required level. This greatly enhances the reliability of the supervisory channel, as it is not affected by malfunction of the high power optical amplifiers.
The data traffic may be sent in a bidirectional manner between two points, utilizing two light guides each having a transmitter and receiver associated therewith. If, however, a single light guide is used for bidirectional working, the supervisory channel preferably carries identifier signals in the event of a malfunction of the light guide, the identifiers used for the two directions of transmission differing. In the case of localized damage to a light guide light transmitted from one end will be partially reflected back from the location of the damage to the transmitting end, whereas light transmitted from the other end of the light guide may be partially transmitted by the localized damage. The use of different identifier signals on the supervisory channel enables the reflected and transmitted signals to be distinguished.